1. Field of the Invention
The present invention relates to a bismuth oxide superconductor and a method of preparing the same, and more particularly, it relates to improvement for a magnetic field property of critical current density in a bismuth oxide superconductor.
2. Description of the Background Art
In recent years, superconducting materials of ceramics, i.e., oxide superconducting materials, are watched as materials which exhibit higher critical temperatures.
For example, a bismuth oxide superconductor, which exhibits a high critical temperature of about 110 K, is expected as a practicable superconducting material.
It is known that a bismuth oxide superconductor has a phase showing a critical temperature of 110 K and those showing critical temperatures of 80 K and 10 K. It is also known that a non-superconducting phase partially appears particularly when a superconductor of a 110 K phase is prepared.
In relation to such a bismuth oxide superconductor, it is further known that the 110 K phase has a 2223 composition in a composition of Bi--Sr--Ca--Cu or (Bi,Pb)--Sr--Ca--Cu, while the 80 K phase has a 2212 composition in the same composition.
In order to apply a superconductor to a cable or a magnet, it is necessary to attain a high critical current density, in addition to a high critical temperature. In particular, it is necessary to ensure a required critical current density in the magnetic field which is applied to the superconductor.
However, a conventional bismuth oxide superconductor is rather inferior in magnetic field property of critical current density. Particularly when the magnetic field is applied in parallel with the c-axis, the critical current density is significantly lowered.